A major constraint to scaling-up antiretroviral therapy (ART) services and achieving universal access to HIV care and treatment in sub-Saharan Africa is the critical shortage of trained healthcare workers. Task- shifting - the redistribution of tasks among the health workforce team from highly qualified staff to less specialized health workers - offers a promising strategy to address this human resource crisis. Overall Goal and Aims: The study goal is to identify effective, scalable, and sustainable models of task- shifting that support high levels of retention and adherence among ART patients in sub-Saharan Africa. The research has two phases: quantitative and qualitative. The aims of Phase I are to 1) quantitatively describe task-shifting characteristics in 18 diverse ART programmes in Tanzania, Uganda, and Zambia, and 2) examine the relationship of task-shifting characteristics and levels of retention and antiretroviral drug adherence. The aim of Phase II is to use a case study approach to qualitatively examine two effective models of task-shifting, exploring issues related to the scalability and sustainability of interventions to support high levels of retention and adherence among ART patients. Study Population and Settings: Phase I involves adult ART patients, 18 years or greater at the start of ART initiation and who have been on 3 ARV drugs for at least six months prior to the start of the study in 18 ART sites in Tanzania, Uganda, and Zambia. Phase II will involve adult ART patient, ART clinic provider, and ART programme and policy stakeholder informants from two ART sites, one in Tanzania and another in Uganda. Design: Phase I will leverage the infrastructure of the Adult ART Retention and Adherence in Tanzania, Uganda, and Zambia study by adding an additional data collection component on task-shifting to the cross- sectional survey for ART clinic managers (n=18), and leverage the study's data by merging and analysing the task-shifting data with the retention and adherence data of ART patients (n=4,500). The retention study is a retrospective medical chart abstraction of 4,500 randomly-selected ART patient files from the clinic, laboratory, and pharmacy. The adherence study is a cross-sectional interview of 4,500 systematically-selected adult ART patients presenting at the clinic. Phase II will use a case study approach to examine two effective models of task-shifting and methods of data collection include: 1) in-depth interviews with providers (n=16- 20), clients (n=16-20), and key stakeholders (n=16-20); 2) collection and content analysis of relevant programme documents; and 3) participant observation of planning meetings, training workshops, and the implementation of task-shifting.